Pressure system



Sept. 7, 1948. VA. E. KITTREDGE PRESSURE SYSTEM Filed Aug. 30, 1944 Patented Sept. 7, 1948 UNITED STATES PATENT OFFICE PRESSURE SYSTEM Arthur E. Kittredge, Audubon, N. J.`

Application August 30, 1944, Serial No. 551,990

2 Claims. l

This invention relates to a pressure system particularly designed for the operation of hydraulic devices such as hydraulic presses.

In the operation of a hydraulic press or some similar hydraulic device, it is essential that a very high pressure be exerted only when the moving ram reaches substantially a nal position of rest. Prior to its attainment of such position, i. e., during its motion for taking up slack or for other preliminary operation, it is generally required that only a relatively minor pressure be exerted.

In the conventional driving of a hydraulic press by th'e use of a pump, the pump is designed to provide a high pressure but, consistent with this and to avoid large pump cost, the pump has only a relatively small volumetric displacement, with the result that the preliminary movement of the ram may take place only very slowly. Thus, if the total stroke of th'e hydraulic press which is requiredl for a particular operation is fairly long, the time required for the complete stroke may be quite considerable and wasteful.

The present invention has as its broad object the provision of a pressure-applying system capable of utilizing a, pump having relatively large displacement but operating with comparatively small head in such fashion that the pressure Wh'ich is supplied to a hydraulic press or the like is -a function of the rapidity of motion of the ram in such fashion that if the resistance to the motion of the ram is low, the ram Will move rapidly, While when the resistance becomes high, the ram will move more slowly but with a corresponding increase of pressure applied thereto with a nal exertion of a maximum pressure when the ram reaches a, nal stalled position,

The foregoing result is secured by associating a pump with a recirculatory system including an eductor. It has been proposed, as in th'e patent to Eddison, 1,350,095, to associate a pump with an eductor for the purpose of unloading the pump to conserve energy when the volumetric demands upon the pump are reduced. This is not, however, the object of the present invention, which is concerned with' the operation of a hydraulic press or the like in the fashion previously indicated to secure a variation in its pressure and in its displacement rate to increase the speed of operation of the press and to make possible the use for this purpose of a pump producing a relatively small head at a large displacement.

The foregoing, and other objects of the invention relating to details of construction and operation, Will be apparent from the following description, read in conjunction with' the accompanying drawing, in which:

Figure 1 is a diagram, having certain parts shown in section, illustrating a multiple stage system provided in accordance with the invention;

Figure 2 is a diagram illustrative of one phase of the operation of the system of Figure 1; and

Figure 3 is a second diagram illustrative of another phase of such operation.

Referring to Figure 1, there is diagrammatically illustrated at 2 a hydraulic press or other device to the ram of which hydraulic pressure is to be applied in such fashion as to cause the exertion of a large force when the ram reaches or approaches a condition of rest. The operating liquid is applied to the press through the line 4. The line 6 represents the supply of liquid which, in ordinary applications, may, for example, be the ordinary pressure water supply available at the point of use. The line 6 is connected through 'I to the intake of a pump 8. The nature of this pump in the present case is quite immaterial and the pump may be either a centrifugal pump or a positive displacement pump with attendant slight differences in characteristics of operation which will be readily apparent to those skilled in the art. Connected to the discharge line 4 from the pump through a line lll is an eductor I4, the nozzle I2 of which is arranged to discharge in the usual fashion into a pressure recovery tube 20 which', in turn, discharges into the line 1 through a connection 22. The throat or mixing chamber I8 of the eductor I4 is connected to the supply line 6 through the connections 26, I'l, and I6. Between the connections Il and I6, th'ere is located a check valve 28, there being also interposed in the line 6 in advance of the connection 22 a check valve 24.

A -connection 30 from the line 4 leads to the nozzle 32 ofl an eductor 34, the mixing chamber or throat 36 of which is connected to the line 6 as indicated at 38. Discharge is effected through' the pressure recovery tube 40 and the connection 42 to the line I6 between the valve 28 and the throat I8 of the rst eductor.

Assuming that the ram of the hydraulic press is at the initial part of its stroke and that there is a minor resistance offered to its movement, the. pump 8 will initially draw liquid through the line 6, check valve 24, and line l to apply to the hydraulic press a pressure which is essentially that in the line 6 increased by the head of th-e pump. Substantially the full volume of liquid handled by the pump may at this time be delivered to the hydraulic press, with the result that the ram Will be advanced rapidly. At the same time, some circulation will take place through the eductor I4 (the capacity of which may be small compared to that of the pump) which will receive liquid from the supply line 6 through the connections 26 and I'I, the check valve 28, and the connection I6. Additionally, some further circulation will take place through the eductor 34 (which may also be small) which, in turn, will receive liquid through the connection 38.

Assume now that a condition is attained due to movement of the ram at which the resistance to its motion exceeds the pressure heretofore mentioned. Under these conditions, its motion would substantially cease. However, the recirculation through the eductor I4 will continue with the resultant building up of a pressure at 22 in excess of the pressure at B, resulting in elosure of the check valve 24 so that the supply of liquid to the system will now occur only through the two eductors.

Under these conditions, the check valve 24 being closed, the system will have substantially the aspect indicated in Figure 2, neglecting the relatively small contribution of the second eductor 34 to the supplying of liquid to the system. By reason of the recirculating system, the pressure at the outlet of the pump may now rise to a value substantially exceeding the previous value so that the ram will again move, less rapidly than before but with a higher applied pressure, until nally the pressure in the line I6 will exceed the supply pressure with resultant closure of the check valve 23 as the resistance to motion of the ram further increases.

When the cheek valve 28 closes, the system attains the aspect indicated in the diagram of Figure 3, in which the sole connection of the system to the source is by way of the eductors 34 and I4 in the staged arrangement indicated in that figure.

The above description is, of course, somewhat idealized and, as a matter of fact, the transition from one phase of operation to the next is a relatively smooth one with a gradual change of the proportions of the flows from the supply through the various passages. In any event, it will be evident that what is involved is a reduction of the rapidity of movement of the ram dependent f upon the resistance offered to its movement while at the same time the pressure on the ram increases. Finally, when the ram reaches its final stationary position in which no further movement is possible, a maximum pressure will be exerted thereon with the pump effecting solely circulation of liquid through the eductors without further entrance of liquid from. the supply. The final conditions attained will become apparent from the following analysis of the pressures reached, assuming rst that the lnal condition is reached with the eductor 34 absent, and later with the eductor 34 present, or possibly with further staging.

Considering rst Figure 2, if P1 is the pump outlet pressure and P2 is the pump inlet pressure, the pump head I-I is Pi-Pz. If Po is the pressure of the supply to the throat of the eductor I4, the various pressures are related at the eductor by:

in which R is the jet recovery ratio characteristie of the eductor.

It follows from the above that H P1=Pu+1 In other words, when the condition of Figure 2 exists, the pressure P1 applied to the hydraulic press cylinder, or the like, exceeds the input line pressure by an amount which may be five to ten times the head of the pump, since R in practice may have a value of about .80 to .90. This also represents the final condition if a single eductor is used.

In the case of operation of the double stage arrangement of Figure 3, i.e., the nal operation of Figure l, a similar analysis leads to:

.in which R1 and R2 are the jet recovery ratios of the tWo eductors. Thus, by staging, a very high pressure may be attained when full load conditions are reached. While triple or further staging is theoretically possible, a practical limit is generally reached with two stages.

It will be clear from the foregoing that the pressure attained may by the use of the present system greatly exceed the sum or" the pressures 6 and the head of the pump. In fact, it will be evident that the pressure at 6 may well be zero or less that the supply of liquid may be lifted from a sump.

The reliei of pressure may be effected in suitable fashion by the use of a valve which need not be illustrated.

What I claim is:

l. In combination with means subject to liquid pressure and attaining a nal condition involving substantially no liquid displacement and in which the pressure applied thereto should be maximum, -a pump connected to said means to apply pressure thereto, an eductor of the jet pump type having its nozzle receiving liquid from the pump, having its discharge connected to the pump to deliver liquid thereto, and having its throat connected to a supply of liquid, a second eductor of the jet pump type having its nozzle receiving liquid from the pump, having its discharge connected to the throat of the irst mentioned eductor, and having its throat connected to a supply of liquid, means including a check valve for supplying liquid from a supply directly to the pump, the check valve being on the supply side `of thc connection between the discharge of the first mentioned eductor and the pump, and a second check valve between the throat of the first mentioned eductor and the supply of liquid to the rst mentioned eductor, the second cheek valve being on the supply side ef the connection between the discharge of the second mentioned eductor and the throat of the rst mentioned eductor.

2, In combination with means subject to liquid pressure and attaining a final condition involving substantially no liquid displacement and in which the pressure applied thereto should be maximum, a pump connected to said means to apply pressure thereto, an eductor of the jet pump type having its nozzle receiving liquid from the pump, having its discharge connected to the pump to deliver liquid thereto and having its throat connected to a supply of liquid, a second eductor of the jet pump type having its nozzle receiving liquid from the pump, having its discharge connected to the throat of the iirst mentioned eductor, and having its throat connected to a supply of liquid, .means for supplying liquid from asupV ply directly to the pump. the last mentioned means including a valve constructed and arranged between the last mentioned supply and the connection between the discharge of the rst mentioned eductor and the pump to interrupt the di Irect supply of liquid to the pump when the discharge pressure ofthe first eductor exceeds the pressure of the last mentioned supply, and a valve constructed and arranged between the first mentioned supply and the connection between the discharge of the second mentioned eductor and the throat of the first mentioned eductor to interrupt the direct supply of liquid to the throat of the rst mentioned eductor when the discharge pressure of the second mentioned eductor exceeds the pressure of the first mentioned supply.

ARTHUR E. KITTREDGE.

6 REFERENCES CITED The following references are of record in the ille of this patent: 

